Encyclopedias are a good starting point for finding background on your topic.  They provide historical context, key people and events, and often cite key works published on the topic.  Bibliographies are also a good way to identify key works, both primary and secondary, or get a good start on a literature review.

Oxford Reference Collection (online encyclopedias, dictionaries) 

Britannica Online
For brief discussions of a country's history, events, major figures, and facts.

Cambridge Encyclopedia of Latin America and the Caribbean
NY: Cambridge UP, 1992.
Refeference F1406 .C36 1992

The Cambridge History of Latin America
Cambridge: Cambridge University Press, 1984 - (multiple volumes).
The last three volumes cover Latin America from 1870 to recent. Each volume includes extensive bibliographical essays which guide the reader to primary and secondary sources.
F1410 .C1834 (stacks)

Encyclopedia of Latin American History and Culture
New York: Scribners, 1996. 5 volume compendium on events, people, places.
Reference F1406 .E53 1996

A Reference Guide to Latin American History
Arnonk, NY: M.E. Sharpe, 2000
Reference F1410 .R395 2000

South America, Central America, and the Caribbean
London: Europa, 1995.
Several page summaries of recent history, politics, and economic conditions in each country. For updated information, see the Europa World Year Book
Reference F1414.2 .S68

Mexico: An Encyclopedia of Contemporary Culture and History
Santa Barbara, CA: ABC-Clio, 2004
Reference F1234 .C67 2004

Country Studies - Library of Congress
For a book length study on an individual country which includes a good historical introduction.

General Bibliographies

American Historical Association's Guide to Historical Literature 
Edited by Mary Beth Norton.
NY: Oxford University Press, 1995. Use Index in vol. 2
Reference D20 A1 A55 1995

Reference Sources in History: An Introductory Guide. 2nd Edition
 
Santa Barbara: ABC-Clio, 2004.
Reference D20 A1 F72 2004 (previous edition in stacks) 

Bibliographic Index
H.W. Wilson. 
Use to identify full-length bibliographies.
Search under specific subject, for example: Vietnam--History.
Reference Z1002 B595 (Library has 1942-current).

Selected Specialized Bibliographies


Latin America and the Caribbean: A Critical Guide to Research Sources

Edited by Paula H.Covington.
NY: Greenwood Press, 1992.
Includes brief essays on topics and extensive annotated bibliography.
Reference F1408 .A1 L27 1992

Latin American Studies: An Annotated Bibliography of Core Works
Jefferson, NC: McFarland, 2002

Latin American Studies: A Basic Guide to Sources
Metuchen: Scarecrow, 1990
Reference F1408 .A1 L324 1990

Encyclopedia of African-American Culture & History: The Black Experience in the Americas
6 volume set searchable as part of the Gale Virtual Reference Library. Covers the U.S., Canada, Latin America, and the Caribbean.